1. Field of the Invention
The present invention relates to a vacuum processing chamber having an isolation valve for preserving a vacuum in one portion of a chamber while allowing maintenance or other access to another portion of the chamber. More particularly, the invention relates to a gate valve that can preserve a vacuum in a portion of a chamber in order to reduce the amount of time necessary to pump down the chamber after maintenance in another portion of the chamber.
2. Background of the Related Art
Vacuum chambers have been used to advantage in many different processes in many different industries. The vacuum conditions and the purpose of the vacuum can vary widely from one process or chamber to another. In many applications, the vacuum chamber will work in cooperation with or actually contain certain equipment or members that will further alter the conditions in the chamber or perform some operation within the chamber. Furthermore, the vacuum chamber will typically contain a workpiece that is being conditioned by the chamber environment or processed by equipment within the chamber. In either case, it is frequently necessary or desirable to replace the workpiece or certain pieces of equipment in the chamber. However, opening the chamber to the surrounding environment eliminates the vacuum, disturbs other conditions in the chamber, allows escape of gaseous components and allows entrance of contaminants.
In order to reestablish a vacuum in the chamber, a variety of pumps, singularly or in combination, may be used according to the specific application to withdraw gases from the chamber. As will be recognized, pumps may be designed to operate over a range of gas flow rates and to achieve a range of pressures. For example, centrifugal pumps are typically used in applications where a high gas flow rate and only a small vacuum pressure is desired. On the other hand, cryogenic pumps are most commonly used in applications where a low flow rate is sufficient and a strong vacuum is desired.
Regardless of the specific application or the type of pump in use, it should be recognized that a significant amount of time and energy can be required to draw a vacuum in the chamber. Typically, the amount of time and energy that is expended ranges from about 5 to about 24 hours and represents a significant loss of productivity and efficiency. Therefore, much research effort has been devoted to increasing the productivity and efficiency of vacuum chambers and the processes that are performed within them. The results of these efforts have taken a number of different directions. For example, in high vacuum applications, such as integrated circuit fabrication, a roughing pump can be used to draw a vacuum on the order of about 10.sup.-3 torr followed by a cryogenic pump to establish a high vacuum on the order of about 10.sup.-7 to about 10.sup.-9 torr. In this manner, the strengths of each pump are utilized to minimize pump time. Another example involves efforts at increasing the reliability and life of equipment within the chamber to extend the frequency in which the chamber must be opened.
Typical vacuum processes used in the fabrication of integrated circuits include physical vapor deposition ("PVD") and chemical vapor deposition ("CVD"). A simplified sectional view of a typical vacuum chamber for physical vapor deposition of metal onto a substrate or workpiece is shown in FIG. 1. The chamber 20 generally includes a chamber enclosure wall 24, having at least one gas inlet 27 and an exhaust outlet 28 connected to an exhaust pump (not shown). A substrate support member 26 is disposed at the lower end of the chamber 20, and a target 22 is received at the upper end of the chamber 20. The target 22 is electrically isolated from the enclosure wall 24 and the enclosure wall is preferably grounded, so that a negative voltage may be maintained on the target 22 with respect to the grounded enclosure wall. A shield 40 may be disposed within the chamber, and may include an annular, upturned wall 41 on which a clamp ring 30 may be suspended over the support member 26 when the support member is retracted downwardly in the chamber.
In preparation for receiving a new semiconductor substrate into the chamber 20, the substrate support member 26 is lowered by a drive mechanism 42 well below the clamp ring and shield, so that the bottom of the support member is close to a pin positioning platform 36. The support member 26 includes three or more vertical bores (not shown), each of which contains a vertically slidable pin 34. When the support member is in the lowered position just described, the bottom tip of each pin rests on the platform 36, and the upper tip of each pin protrudes above the upper surface of the support member. The upper tips of the pins define a plane parallel to the upper surface of the support member for receipt of a substrate thereon.
A conventional robot arm (not shown) carries a substrate 12 into the chamber 20 and places the substrate above the upper tips (not shown) of the pins 34. A lift mechanism 43 moves the pin platform upwardly, to place the upper tips of the pins against the under side of the substrate and additionally lift the substrate off the robot blade. The robot blade then retracts from the chamber 20, and the lift mechanism raises the support member so that the pins slide down in the support member 26, thereby lowering the substrate onto the top of the support member.
The lift mechanism 42 may continue to raise the support member 26 so that the periphery of the substrate contacts the clamp ring 30 resting on the upturned wall portion 41. The inner diameter of the clamp ring is typically sized slightly smaller than the inner diameter of the substrate to shield the edge of the substrate. The support member may continue moving upwardly to position the substrate a set distance from the target surface.
In the case of the exemplary sputtering chamber 20 shown in FIG. 1, the deposition process is initiated by supplying a sputtering process gas (typically argon) to the chamber through the gas inlet 27, and applying a negative voltage from a DC power supply 21 to the sputtering target 22. The voltage excites the argon gas into a plasma state, causing the argon ions to bombard the negatively biased target to sputter material off the target. The sputtered material then deposits on the substrate, except for a portion of the material which is deposited on the shield, clamp ring, or other internal surfaces or components of the chamber. After the film layer has been deposited on the substrate, the substrate is removed from the chamber 20 by reversing the sequence of steps by which it was carried into the chamber.
While certain improvements in the chamber design and chamber consumables, such as the target 22, have increased the productivity and efficiency of vacuum chambers, further improvements are desired. Therefore, there remains a need for a vacuum chamber that reduces the amount of time required to draw a vacuum after replacing consumables or performance of routine maintenance. It would be desirable if the chamber could preserve the vacuum in the chamber. More particularly, it would be desirable to have a chamber that isolates a frequently replaced consumable or component from the rest of the chamber so that only a minimal portion of the chamber is exposed to the surrounding environment and the volume of space that must be evacuated is minimized.